1. Field of the Invention
The present invention relates to a catalytic combustion reactor and a catalytic structure, each of which, when a gas is subjected to catalytic combustion reaction, effectively recovers thermal energy generated by the catalytic combustion reaction under an atmosphere having a high temperature or having a high temperature and a corrosive property, and each of which is particularly adequate for oxidation reaction of hydrocarbon and/or halogenated hydrocarbon, and a method for carrying out catalytic combustion reaction by using the catalytic combustion reactor and the catalytic structure.
2. Description of the Background
Catalytic combustion reactors are broadly classified into a fixed bed type, a fluidized bed type and a moving bed type in terms of shape. Among them, fixed bed catalytic combustion reactors have been widely adopted in the chemical industry. As described on page 1118 of “Kagaku Kohgaku Binran, 5th revised edition”, the fixed bed catalytic combustion reactors are further classified into a) a thermal insulation type, b) a multi-stage and thermal insulation type with heat exchange made in an intermediate step, c) a multi-stage and thermal insulation type with a raw material supplied in an intermediate step, d) an autothermal type, e) a multi-tube heat exchange type and f) a direct heating type in terms of heating methods. The heating method is selected, depending on the magnitude of heat generated by the reaction.
In general, when oxidation reaction is carried out in a fixed bed catalytic reactor, a method for using a heat exchanger to carry out heat exchange between a fluid flowing into and a fluid flowing out of a thermal insulation type reactor in addition to the autothermal type among the classified types is adopted as a method for recovering the reaction heat since the fluid that has passed through the catalytic bed is heated to a high temperature by the reaction heat.
When reaction accompanied by the creation of a corrosive gas, such as oxidation reaction of halogenated hydrocarbon, is carried out, a gas having a high temperature and a corrosive property is created. When the reactor is made of a metallic material in such a case, the portion of the reactor in contact with that sort of fluid needs to be made of a so-called quality material having a superior corrosive-resistant property, such as an Fe-based alloy containing high Ni and high Cr, or a Ni-based heat-resistant and corrosion-resistant alloy containing Cr.
The fixed bed catalytic reactor needs to have a catalytic structure located therein so as to equally increase the throughput of a fluid per unit catalyst amount, or a so-called space velocity, improving catalytic efficiency and equalizing the lifetime of catalysts. Additionally, the catalytic structure needs to be located so as to minimize the pressure loss in the catalysts per se in order to provide smooth communication of a fluid to be subjected to combustion reaction.
JP-A-10-156142 discloses a catalytic purifier, which purifies air containing a toxic gas to obtain clean air having a high temperature by using a catalytic combustion reactor to burn and purify the toxic gas contained in the air to be purified, and which includes at least a heat exchanger for preheating the air to be purified with purified air having a high temperature, a preheater used on start-up, a feed device for a combustible material, and a catalytic combustion reactor so as to flow the air to be purified through the devices in this order. In the purifier of JP-A-10-156142, the reactor main body and the external communicating pipe for introducing the purified gas having a high temperature to the heat exchanger are configured to be exposed to the purified gas having a high temperature after combustion reaction.
U.S. Pat. No. 5,466,421 discloses an exhaust gas purifier, which comprises a cylindrical reactor casing, a heat exchanger, a pipe for introducing an exhaust gas to be treated into the heat exchanger, and a pipe for discharging the treated exhaust gas from the casing, wherein the heat exchanger includes a first branch pipe and a second branch pipe having a limitation to thermal contact. The purifier of U.S. Pat. No. 5,466,421 is configured so that an outermost portion of the reactor main body is exposed to the purified gas having a high temperature between the outlet of a catalyst bed and a housed tube bundle as shown in FIG. 2.
Although each of the catalytic reactors disclosed in those prior art references preheats a fluid to be treated by use of a purified gas having a high temperature after combustion reaction in the heat exchange associated with the reactor, no consideration is given to thermal energy loss due to heat radiation, which is created by the contact of the outer shell with the reactor main body and the pipe passing the purified gas having a high temperature therethrough, and no consideration is given to a decrease in the area of a portion in contact with a fluid having a high temperature or having a high temperature and a corrosive property.
Although JP-B-51-7245 discloses a catalytic purifier, which provides a catalyst in slant fashion therein in order to increase the contact surface to raise catalytic efficiency, no consideration is given to the recovery of reaction heat as a preheating source for a fluid to be treated or a decrease in the area of a portion in contact with a fluid having a high temperature or having a high temperature and a corrosive property.
Although JP-A-56-97525 discloses a contact oxidation system for a contaminant in an exhaust gas, which is characterized to comprise a treatment chamber including a gas-permeable catalyst bed including a first catalyst layer and a second catalyst layer containing at least one kind of noble metal, no consideration is given to the arrangement for increasing catalytic efficiency. No consideration is given to the recovery of reaction heat as a preheating source for a fluid to be treated or a decrease in the area of a portion in contact with a fluid having a high temperature or having a high temperature and a corrosive property.
JP-A-5-39912 discloses a deodorizing system, which burns a fluid to be treated containing a harmful component, such as a malodorous substance, or dust and dirt, and kills germs in the fluid to be treated, and which comprises a heat exchanger for preheating the fluid to be treated by purified air having a high temperature, a burner for throwing flame into a combustion chamber, and a porous ceramic plate for directing an untreated gas in zigzag fashion in an atmosphere having a high temperature in the combustion chamber to sufficiently provide the untreated gas with radiant heat. In the reactor of JP-A-5-39912, a direct burning system without using a catalyst is adopted. No consideration is given to the improvement in maintenance by independently providing the combustion chamber and the tube bundle.
Although JP-U-6-30415 discloses a catalytic system for purifying an exhaust gas from a diesel engine, wherein a fluid to be treated is passed from the inside of a cylindrical catalyst or two rectangular catalysts to outside or vice versa to decrease the amount of soot adhering to the cylindrical catalyst or the rectangular catalysts, no consideration is given to the location of the catalyst or catalysts for increasing catalytic efficiency. No consideration is given to the recovery of reaction heat as a preheating source for the fluid to be treated or a decrease in the area of a portion in contact with a fluid having a high temperature or having a high temperature and a corrosive property.